Development for Measuring Mass Concentration and Size Distribution in Micro Particle Sensor

IAQ (indoor air quality) is an important indicator for determining indoor microclimate and comfort. The indicator depends on the amount of pollutants in the air. The air pollutants refer to suspension with very small particles in the air. The optical instrument is the de-facto way to measure the concentration of particles in the air. Nevertheless, the design of such instrument is often too complicated to decrease its volume. In addition, the density of the particles must be known a priori in order to calculate weight concentration. It thus limits its capability to examine the weight of particles with mixing materials.
The objective of this work is to develop a miniature particle sensor to detect the distribution of particles and concentration of weight of each particle size in the air, and try to develop the element of sensors by different principles at the first stage of this work. These include Piezoresistive Cantilever particle sensor, Light Blockage particle sensor, and Capacitance particle sensor. At the second stage of this work, we made the element of particle size distribution by the conception of Virtual Impactor, and QCM (Quartz-crystal microbalance) is used to measure the mass of particle loading by utilizing its characteristic of resonance frequency shift. We integrate the frame of those two devices and find the property of them by experiment. Finally, we have designed and fabricated the particle sensor which can sort out the particle size and measure the mass of particle.
Several insights were gained in this work. In Piezoresistive Cantilever particle sensor, we found that the stiffness of cantilever is too high to be deformed. If we can decrease its stiffness and use the CMOS circuit and conception of statistics, we can produce the particle sensor which can measure the size and number of particle. In Light Blockage particle sensor, although we could not calculate the number of particles by the voltage difference, we were able to count the number of particles by observing the peak number of the curve of the output voltage. The variation of capacitance in Capacitance particle sensor was too small to detect the small size particles. Nevertheless, it might be useful to detect particles with larger size or larger dielectric constant.
Virtual Impactor developed in this work could be used to classify particle diameter in three different ranges, <2.282μm, 3.15~2.282μm, and >3.15μm. We have also identified the characteristic curve of QCM for mass detection. Using QCM with virtual impactor, we have demonstrated a sensing prototype to calculate the mass of particles adhering to QCM.